<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Parsing</title>
    <script src="https://code.jquery.com/jquery-2.1.4.min.js"></script>
    <script defer>


        // 1000000 primes
    /*    document.addEventListener('DOMContentLoaded', function () {
            document.body.firstElementChild.innerHTML = 'First Div';
        });
*/
    </script>
</head>
<body>
    <div>

    </div>
    <script>

        var xhr = new XMLHttpRequest();
        xhr.open('get', '/customers');
        xhr.setRequestHeader('Accept', 'application/xml');
        xhr.send();

        // json
        // xml

        // backend
        // req --> headers, body, params, query
        // req.headers['Accept'] --> 'application/json'
        // res.set('Content-Type', 'application/json');

    </script>
</body>
</html>